Waveguide transducer



March 14, 1961 SCHARFMAN WAVEGUIDE TRANSDUCER Filed Sept. 50, 1957 Fle. 9

M Y E W A EH.O WQW I A 0 w w ov HB United States Patent Office 2,975,380 Patented Mar. 14, 1961 WAVEGUIDE TRANSDUCER Howard Scharfman, Lexington, Mass., assignor to Raytheon Company, a corporation of Delaware Filed Sept. 30, 1957, Ser. No. 687,101

9 Claims. (Cl. 333-9) This invention relates to Waveguide transducers, and, more particularly, to broadband waveguide transducers capable of coupling two sources of electromagnetic energy propagated in two orthogonal modes into a common waveguide structure, which supports such crosspolarized modes, and to transducers which propagate said electromagnetic wave energy in said waveguide structure.

In numerous microwave applications it becomes de sirable to transmit more than one signal in a waveguide from a plurality of broadband frequency sources by utilizing cross-polarized electromagnetic modes as separate information channels. In systems wherein such dualmode propagation is desirable, it is also desirable to transmit electromagnetic energy in one mode over a relatively broad band of frequencies entirely independent of the other transmitted broadband mode. However, in applications in which a dual-mode waveguide transducer is formed by connecting a side arm of rectangular wave guide to a main section of waveguide, the waveguide sections being joined in a plane parallel to either the E or the H vectors of the energy propagated by both guides, energy introduced into the rectangular arm will split at the junction and propagate in both directions in the main section of waveguide unless an appropriate short circuit or reflecting structure is placed in the guide to force the energy to propagate in a single direction. However, it has been found that a device of this type cannot be operated efficiently over a broad band of frequencies. In numerous applications, therefore, it would be desirable to provide a broadband transducer in which electromagnetic wave energy may be introduced into one input arm in a mode cross-polarized to energy introduced into the other input arm, and propagate said energy over a broad band of frequencies along a common waveguide structure or transmission line without introducing interaction between the separately transmitted electromagnetic waves.

In accordance with the invention, a dual-mode wide band transducer for electromagnetic wave energy, in which two separate broadband cross-polarized signals may be combined for independent transmission in a common waveguide without undesirable interaction or loss of power, can be achieved by adding a series of reflecting posts, preferably of conductive material, to a T-junction comprising a section of square waveguide having an in put and an output port and a rectangular input arm connected to one side of the waveguide and cross-polarized with respect to the E vector of linearly polarized energy entering input port of the main section of waveguide. One such post is mounted in the transducer or T-junction approximately on the center line of the main waveguide section and offset a short distance from the projection of the center line of the input arm and perpendicular to the main axis of both guides. Two other posts are mounted in the main waveguide, also perpendicular to the axis of both sections of waveguide, and on either side of the first post. These posts are electrically connected to the opposite walls of the main waveguide and are spaced apart from the first post a distance of approximately onequarter the width of the main waveguide. One of the posts is positioned approximately on a projection of a side wall of the input arm and approximately one quarter of the width of the main waveguide from the side of the main waveguide opposite the junction of input arm and waveguide.

The third post is located approximately equidistant from the first or center-line post along a plane extending longitudinally parallel to the axis of the main waveguide and at the junction of an arcuate plane extending through the other two posts. In this manner, a gentle bend of electromagnetic energy entering the input arm is achieved by the diagonally spaced posts which operate in the manner of a 45 angle mirror to reflect radiation in one direction along the main waveguide. While these posts perform the function of complicated reflecting surfaces with reference to energy entering the input arm they are, as noted, spaced apart approximately one-quarter of the height of the main waveguide to cancel or minimize the reflections and the discontinuity eflect connected with cross-polarized energy entering the port in the main guide and passing by the posts.

The invention further discloses a modification of the above-described dual-mode transducer in which the square waveguide and rectangular input or side arm are replaced by a circular waveguide and a rectangular input arm, the energy introduced into the main waveguide being coupled through a polarizing aperture into the circular section of waveguide and passing therethrough unalfected by waveguide posts or pins which are positioned parallel to the E vector of the electromagnetic energy in the rectangular guide, and perpendicular to the E vector of the electromagnetic energy propagated in the main guide. In like manner, these posts which electrically connect the sides of the main waveguide, reflect energy arriving from the input arm in a single direction along the main guide without any interaction with cross-polarized electromagnetic energy traveling along the main waveguide in a similar direction from the input port. Thus, the transducer achieves high order of isolation between two broadband channels of electromagnetic energy traveling in the common waveguide. For example, the input arms operate independently over a band of frequencies in the order of 23 percent of the geometric means frequency entering the transducer.

Other objects and advantages will be readily perceived upon analysis of the drawing, in which:

Fig. l is an isometric view of the transducer of the invention;

Fig. 2 is a side view of the transducer of the invention;

Fig. 3 is a top view of applicants transducer;

Fig. 4 illustrates a second embodiment comprising a circular waveguide having a rectangular waveguide arm connected thereto;

Fig. 5 is a top Fig. 4;

Fig. 6 is a cross-seetional view of the transducer structure shown in Fig. 5 taken along the line 6-6 of Fig. 5;

Figs. 7 and 8 are diagrammatical views showing the electromagnetic E vector propagating in a square and circular waveguide; and

Fig. 9 is another embodiment illustrating a method of using the invention in connection with a dielectric-filled waveguide structure.

In Figs. 1 and 2, the reference numeral 10 designates a section of square waveguide having walls 11 and 12 electrically connected to oppositely disposed walls 13 and 14 to form a square waveguide having a linear polarization guide 29 of rectangular configuration at the input end of the waveguide section. The walls 11 and 12 are parallel to the E vector of the propagated energy from a source of microwave energy 9, as shown in Fig. 1.

view of the embodiment shown in A second section of waveguide 15 having oppositely disposed walls 16 and 16a, 17 and 17a joins the first section at an opening in wall 13 to form an input arm fed by a separate source of microwave energy 8 connected to the main waveguide section 10. The input arm 15 comprises a rectangular guide which polarizes energy at right angles to the energy entering the input port 29. Moreover, the H plane of the energy propagated in each waveguide and the axes of the two guides are at right angles at their junction. Three matching or reflecting posts 18, 19, and 20 are mounted in the main section of waveguide 10, and extend in a direction perpendicular to the wall 11. One of said reflection posts, 19, is positioned along the center line of the main waveguide section 10 at a point offset from the projection of the center of the input arm by the distance a, as shown in Fig. 2, which is equal to approximately one-sixth the width of the input arm 6a. One of the other matching posts 18 is positioned approximately one-quarter of the width of the side 11 and 12 from the top wall 13 of the main waveguide section and adjacent to a projection of one of the walls 17a of the input arm, 15, as indicated by the line 21 in Fig. 2. The third reflecting post 20 is positioned approximately one-quarter of the distance from the lower main waveguide wall 14 and approximately in an arcuate plane extending through the first two posts 18 and 19. In this manner, a linearly polarized wave at the rectangular waveguide input port 29 and at the input arm 16 are propagated along the common waveguide 10 without interaction and over a band width of approximately 23 percent of the carrier frequency. The forementioned posts function as complicated reflecting surfaces in the modified T junction, which in operation acts very much like the Y junction described on pages 273 and 274 of vol. 14 of the Radiation Laboratory Series, entitled Microwave Duplexers, by Smullin and Montgomery. However, in the Y junction, the energy is dispersed from the input arm in two directions along the waveguide, the posts forming a compound wedge inserted into the T shape junction. In the present embodiment, the posts or rods simulate a bend or reflector in the guide in a manner in which energy entering the input arm 15 is reflected in a single direction along the main waveguide 10 without any appreciable portion being diverted in the opposite direction. On the other hand, energy coming from the other end of the guide 10 is propagated down the guide with no appreciable portion of the energy being diverted by the cross-polarized input arm 15. In fact, the input arm 15 may be shorted, since the two input arms operate substantially independent of each other over a wide band of frequencies. While the position of the matching posts 18, 19 and 20 of Figs. 1 and 2 are shown forming a gentle or arcuate bend, they may be shifted by being bent from their present position, as specified above, to permit the junction to operate efliciently over as broad a band of frequencies as possible. In some instances, two or more matching posts may be positioned either in a plane or in an arcuate plane and the transducer will still operate over a wide band of frequencies at close to maximum efliciency.

The posts or rods are preferably constructed of a metallic material, the diameter of which preferably should not have a cross-sectional area with respect to the area of waveguide covered by the input wave of more than approximately a l-to-3 ratio. In order to minimize mismatch problems or reflections from energy coming from the input port, the rods can be positioned in the manner shown and holes drilled of the same diameter as the rods through the waveguide. The rods are then inserted through the holes into the waveguide and firmly attached in place as, for example, by soldering. By this structure the matching posts or rods may easily be inserted in the waveguide and their efiect on the waveguide may be finely adjusted by slightly bending the rods to the position of minimum discontinuity with respect to energy flowing through the junction.

Referring now to Fig. 3 the relative position of the posts or rods with respect to energy traveling into the input arm 15 is shown. The simulated bend or reflector of energy entering the input arm, which is polarized at right angles to the energy propagating along the main waveguide, is shown, in which the center post 19 is offset from the center line of the input arm by approximately one-sixth the width (1 of the input arm 60, While the post 18 is positioned approximately on the projection of the wall 17a of the input arm.

Referring now to Figs. 4, 5 and 6, another embodiment of a two-mode transducer is shown comprising a circular section of waveguide provided with a rectangular input arm 33 to which is attached a flange 34 to provide a connection with a second microwave source of energy, such as a magnetron or klystron oscillator, as shown at 35, connected by way of rectangular waveguide 36 and flange 37 to the circular waveguide flange 38 by screws 59 inserted in tapped holes 60. The rectangular waveguide 36 will accept and support only TE waves in which the electric vector, which determines the plane of polarization of the Wave, is parallel to the short side of the rectangular waveguide.

The input arm 33 is polarized at right angles to input arm 36 and to three matching posts or pins, 40, 41, and 42 joining the opposite sides of the circular waveguide and separated at a distance one quarter the width of the guide apart. Energy entering arm 33 is bent in the direction of an output flange 39 and propagated along the guide at right angles. The energy entering from arm 36 in which the electric vector, which determines the plane of polarization of the wave, is parallel to the short side of the rectangular waveguide. The output flange 39 is provided to connect microwave energy to a load by means of holes 61. Therefore, microwave energy of the TE mode introduced into waveguide 36 will flow through the two-mode transducer and into a load circuit, not shown, connected to the output flange 39.

Fig. 5 shows a top view of the microwave transducer showing a relative location of pins 40, 41 and 42, looking into the input arm 33.

Fig. 6 shows a side view of the posts positioned in approximately the sazne relative location as in the circular waveguide shown in Fig. 1. Thus, the transducer may consist of waveguide of either square, circular or ridged configuration so long as the orientation of each side arm is chosen so that only the dominant energy mode in each can be propagated. While the plurality of reflecting pins may be placed in the square waveguide shown in Fig. 1 at a one-quarter wave length spacing with respect to input electromagnetic energy as produced from the separate electromagnetic source 9, the number and spacing of pins is not as critical as when the waveguide section consists of circular guide. This is because the electromagnetic vector 51 is at right angles to pins 18 and 20, as shown in Fig. 7, on either side of pin 19. Thus, for any position of the pins shown in Fig. 7, the E vector is disposed at right angles to each pin, while in a section of circular waveguide, as shown in Fig. 8, the E vector extending through the axis is the only vector which is positioned at right angles to a plurality of pins. The curved vectors 52, as shown, would create discontinuity within the circular waveguide 53 unless the proper symmetry of the pins 18 and 20 is observed with reference to pin 19, where the E vectors are not shown perpendicular to every reflecting post. Moreover, other discontinuities will result unless the spacing and location of the three pins are arranged to minimize reflection.

Referring now to Fig. 6, the cross-sectional view of the two-mode circular and rectangular transducer is shown with the pins 40, 41 and 42 spaced apart one-quarter wave length of the guide and extending along an arcuate plane, as previously described, tending to bend the energy entering the input arm 33 toward output flange 39 without any interaction with energy transmitted from energy source 35 through circular waveguide 32. While square and circular waveguides have been shown, in the above embodiments it should be understood, as noted, that ridged waveguide may also be used, the matching pins extending within the guide in a manner similar to that shown in Fig. 1.

Referring now to Fig. 9, it may be desirable to introduce energy from an input arm 60 of relatively small cross-section into a section of waveguide 61 having relatively large cross-section. The section of waveguide 60 is loaded with a dielectric material 62, such as Teflon, which is adapted to support electromagnetic energy in the smaller structure. In this case, matching pins 70, 71 and 72, corresponding to similar matching pins 40, 41, and 42, shown in Fig. 6, are spaced within the projection of the arms of the input section 60 in a manner similar to that shown in Fig. 6, while their position perpendicular to the E vector propagated in the main waveguide remains at a distance apart of approximately one-quarter the width of the Waveguide. Thus, linearly polarized energy entering input arm 60 combines with energy entering the circuiar waveguide 61 by way of input flange 63 and travels along the common section of waveguide in the direction of output flange 64. In this manner the two-mode transducer may be used for transferring energy from separate sources in circular or square waveguide without producing any substantial interaction or discontinuity. Also, the waveguide section 61 may be loaded with dielectric material instead of input arm 60 and similar operation is obtained.

Furthermore, electromagnetic wave energy propagated in two modes along the waveguide in the direction of the two input arms may be extracted from each of said arms according to whether or not the E vector of energy in one mode is perpendicular to the reflecting posts. Thus, energy transmitted along the waveguide in separate channels may be extracted and fed to separate waveguide structures by means of the transducer without undesirable interaction between the two modes.

For the foregoing reasons it is to be understood that the above described arrangements are illustrative of the application of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of the invention. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. A waveguide transducer comprising first and second sections of waveguide with the opposite sides of both waveguides extending parallel to a plane containing the axes of both sections, and with their axes perpendicular to each other and an opening in the sidewall of the first waveguide where the second waveguide joins, a first reflecting post extending across and electrically connecting points on opposite sides of said first waveguide and positioned on the center line thereof at a point offset from the projection of the center line of the second waveguide by a distance approximately a sixth of the width of the seCOIlCl guide, a plurality of reflecting posts located on either side of the first post perpendicular to and electrically connecting opposite sides of said first waveguide, all of said posts positioned in an arcuate plane extending from the junction of said first and second sections of waveguide in a direction diagonally toward the projection of the opposite side of said first section of waveguide onto the opposite side of said second section of waveguide.

2. A waveguide transducer comprising first and second sections of waveguide with the walls of both waveguides parallel to a plane containing the axes of both sections, and with their axes perpendicular to each other and an opening in the sidewall of the first waveguide where the second waveguide joins, a first reflecting post extending across and electrically connecting points on opposite sides of said first waveguide and positioned on the center line thereof at a point otlset from the projection of the center line of the second waveguide by a distance approximately a sixth the width of the second guide, a pair of reflecting posts located on either side of the first post perpendicular to and electrically connecting opposite sides of said first waveguide, each post positioned along a plane longitudinal to the axis of the first waveguide approximately one quarter the width of the first waveguide on either side of the center line of said waveguide, one of said posts positioned along said plane at the junction of a plane defined by the projection of a sidewall of said second waveguide, and the other of said posts positioned approximately equidistant from said first post along said other plane longitudinal to the axis of the first waveguide at the junction of a plane extending through the other of said posts.

3. A device for propagating electromagnetic wave energy along a common waveguide structure in independent cross-polarized modes comprising a source of electromagnetic energy, a section of circular waveguide supporting said electromagnetic wave energy in a plurality of modes, an input port coaxially disposed with respect to said circular waveguide and adapted to linearly polarize said electromagnetic wave energy passing therethrough, a rectangular input arm extending at right angles to said circular waveguide and adapted to transmit energy into said circular waveguide in a mode cross-polarized with respect to energy from said input port, and a single set of reflecting posts positioned in said waveguide opposite said input arm and perpendicular to the E vector of electromagnetic wave energy passing through said waveguide structure from said input port, and parallel to the H vector of electromagnetic wave energy passing through said input arm, said posts further positioned in a single arcuate plane extending from the junction of the side of said input arm and side of said circular waveguide in a direction diagonally toward the projection of the opposite side of said input arm on the opposite wall of said circular waveguide, the centrally located post of said set of posts positioned on the center line of said circular waveguide and offset a short distance from the projection of the center line toward the projection of the side wall of said rectangular input arm onto said center line of said circular waveguide.

4. A waveguide transducer comprising first and second sections of square waveguide with the walls of both guides parallel to a plane containing the axes of both sections, and with their axes perpendicular to each other and an opening in the sidewall of the first guide where the second guide joins, a first reflecting post positioned perpendicular to and electrically connecting opposite walls of said first guide and positioned on the center line thereof at a point offset from the projection of the center line of the second guide by a distance approximately a sixth the width of the second guide, and a pair of reflecting posts located on either side of the first post perpendicular to and electrically connecting opposite walls of said first guide, and positioned along a pair of planes longitudinal to the axis of the first guide approximately one quarter the width of the first guide on either side of the center line of said guide, one of said posts positioned along said plane at the junction of a plane defined by the projection of the side wall of said second guide on the side on which said first post is offset from the center line of said second guide, and the other of said posts positioned approximately equidistant from said first post along said plane longitudinal to the axis of the first guide at the junction of a plane extending through the other of said posts.

5. A waveguide transducer comprising first and second sections of square waveguide with the walls of both guides parallel to a plane containing the axes of both sections and with their axes perpendicular to each other and an opening in the sidewall of the first guide where the second guide joins, a first reflecting post of conductive material positioned perpendicular to and electrically connecting opposite walls of said first guide and poistioned on the center line thereof at a point offset from the projection of the center line of the second guide by a distance approximately a sixth the width of the second guide, and a pair of reflecting posts of conductive material located on either side of the first post perpendicular to and electrically connecting opposite walls of said first guide, and positioned along a pairof parallel planes longitudinal to the axis of the first guide approximately one quarter the width of the first guide on either side of the center line of said guide, one of said posts positioned along said plane at the junction of a plane defined by a projection of the wall of said second guide on the side on which said first post is offset from the center line of said second guide, and the other of said posts positioned approximately equidistant from said first post along said plane longitudinal to the axis of the first guide at the junction of an arcuate plane extending through the other of said posts.

6. A waveguide transducer comprising a first section of waveguide having an input port and an output port and adapted to support electromagnetic energy, said input and output ports coaxially disposed with respect to said first section of waveguide, an input arm fixed to one side of said first section of Waveguide, a single series of conductive posts positioned perpendicular to and electrically connecting opposite walls of said first section of waveguide opposite the aperture in said input arm and arranged perpendicular to the axis of said input arm, said posts spaced apart approximately one quarter the width of the first section of waveguide in a plane extending from approximately the junction of one side of the input arm and the first section of waveguide in a direction toward the projection of the opposite wall of said input arm and the wall of the first waveguide remote from said input arm aperture, said plane extending perpendicular to the longi tudinal axis of said first section of guide, the centrally located post of said series of posts positioned on the center line of said first section of waveguide and offset a short distance from the projection of the center line toward the projection of the sidewall of said input arm onto said center line of said first section of waveguide.

7. A waveguide transducer comprising a first section of waveguide having an input port and an output port and adapted to support electromagnetic energy in two modes, said input and output ports coaxially disposed with respect to said first section of waveguide, an input arm fixed to one side of said section of waveguide, a single series of reflective posts perpendicular to and electrically connecting opposite walls of the first section of waveguide opposite the aperture in said input arm and arranged perpendicular to the axis of said input arm, said posts extending in a plane from approximately the junction of one side of the input arm and the first section of waveguide in a direction toward the projection of the opposite wall of said input arm and the wall of the first section of waveguide which is remote from said input arm aperture, the centrally located post of said series of posts positioned on the center line of said first section of waveguide and offset a short distance from the projection of the center line toward the projection of the sidewall of said input arm onto said center line of said first section of waveguide.

8. A waveguide transducer comprising a first section of circular waveguide having an input port and an output port and adapted to support electromagnetic energy in two modes, said input and output ports coaxially disposed with respect to said first section of Waveguide, a rectangular input arm fixed to one side of said waveguide section, a first conductive pin extending through the axes of said circular waveguide perpendicular to and electrically connecting the opposite sides thereof, said pin oriented perpendicular to the axis of said rectangular input arm, and second and third pins extending parallel to said first pins to form therewith a single set of pins and spaced apart a distance equal to one quarter the Width of said circular guide on either side of said first pin along an arcuate line extending approximately diagonally from the junction of one side Wall of the rectangular guide and circular guide in a direction toward the projection of the other side wall of said rectangular guide on the wall of said circular guide remote from said aperture, where by energy propagated in said input arm directed toward the output port of said circular guide is cross-polarized to energy propagated along said circular guide, the centrally located pin of said set of pins positioned on the center line of said circular guide and offset a distance from the projection of the center line toward the projection of the side wall of said input arm onto said center line of said circular guide.

9. A waveguide transducer comprising a section of waveguide having an input port and an output port, an input arm fixed to one side of said waveguide section, separate sources of electromagnetic energy coupled through separate polarizing apertures to said input arm and input port, a single set of conductive posts positioned in said first section of waveguide opposite the junction of said input arm in a manner perpendicular to the axis of said section of waveguide and perpendicular to the axis of said input arm, said posts spaced :1 quarter of the width of said section of waveguide apart from each other and from one of said posts positioned on the center line of said section of waveguide, said posts extending in a diagonal manner from the junction of one side of said input arm and waveguide section to the projection of the opposite side of said input arm and the other side of said section of waveguide, thereby to reflect energy from said input arm in a single direction along said waveguide, the centrally located post of said set of posts positioned on the center line of said waveguide section and offset a short distance from the projection of the center line toward the projection of the side wall of said input arm onto said center line of said waveguide section.

References Cited in the file of this patent UNITED STATES PATENTS 2,364,371 Katzin Dec. 5, 1944 

